What is this test?
TSH is a pituitary hormone that controls the production of thyroid hormones by the thyroid gland.
Why might it be ordered?
- For initial evaluation of symptoms of decreased or increased thyroid function.
- To monitor thyroid hormone treatment or treat increased function.
What sample is needed?
A healthcare professional collects a venous blood sample. Depending on the method, the laboratory uses serum or plasma.
How should you prepare?
For follow-up testing, try to have samples collected at a similar time and under similar conditions. Report the timing of your thyroid medicine and whether you take biotin. Tell the laboratory about all medicines, hormone treatments, vitamins and supplements you take. Do not stop or change treatment unless your clinician tells you to. Follow any instructions about fasting and the time of collection.
How should you understand the result?
TSH shows how the pituitary gland is responding to thyroid hormones, but it does not identify the cause of an abnormal result. It is usually interpreted with FT4 and sometimes FT3 and thyroid antibodies. Your result is interpreted using the reference interval on the laboratory report and in the context of your symptoms, medical history and other test findings.
Sources and editorial status
This patient-facing text is an editorial draft. It should be approved by a laboratory physician before official publication.